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BGV Vertex Resolution First Analysis Vertex Resolution as Function of Aperture

BGV Vertex Resolution First Analysis Vertex Resolution as Function of Aperture. M. Kuhn, P. Hopchev. Introduction. a im at 0.2 aim at 10 %. Actual transverse beam size for Gaussian shaped beams is broadened by vertex resolution When : goal for final BGV! Motivation:

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BGV Vertex Resolution First Analysis Vertex Resolution as Function of Aperture

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  1. BGV Vertex Resolution First AnalysisVertex Resolution as Function of Aperture M. Kuhn, P. Hopchev Maria Kuhn - BGV Meeting #20 - 25.9.2013

  2. Introduction aim at 0.2 aim at 10 % Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Actual transverse beam size for Gaussian shaped beams is broadened by vertex resolution • When : goal for final BGV! • Motivation: • Measurement at 7 TeV most challenging, as the beam is smallest • Goal of initial BGV system: demonstrate the principle • vertex resolution ~7 TeV beam (150-200 mm) would be sufficient • Analyse vertex resolution as function of • Beam pipe radius: 23 mm, 21 mm and 19 mm aperture • Exit window tapering angle: 45º and 75º

  3. Input for MC Simulation and Vertex Reconstruction BGV sche-matic detector layout Maria Kuhn - BGV Meeting #20 - 25.9.2013 • See talk in BGV meeting #17 (14/08/2013) • Proton beam – neon gas target interactions simulated with HIJING • Flat distribution of events in z-range [-500;1100] mm • Process ~ 73000 events with large number of high multiplicity tracks • 2 detector modules at z = 1591 mm and z = 2611 mm with 2 space point measurements per station • Variable exit window thickness • Thickness with R = 23 mm : 0.75 mm, thickness with R = 106 mm: 3.5 mm, linear interpolation in between

  4. Cut on Track Multiplicity NTr (I) P. Hopchev Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Vertex Resolution improves with track multiplicity (NTr) • When measuring the beam profile, select events with high #tracks • What is the expected rate, where we should cut on the NTr? • Determine total inelastic interaction rate per bunch: • Assuming: 2808 bunches per beam () • Ne gas flat over (gas target length) • (0.45/7 TeV)

  5. Cut on Track Multiplicity NTr(II) P. Hopchev Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Freduct indicates what fraction of the events is needed to retain in order to get 200/20000 events per 3 min • i.e. to get 5/0.5 % statistical error on the beam profile fit (assuming Gaussian) • Subsequently, we can tell what NTrcan be reached • Caveat: large uncertainty associated to the distribution tails (when a very small fraction of events is selected)

  6. Cut on Track Multiplicity NTr (III) Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Guidelines for BGV vertex resolution study with toy MC: • For detector layout with SciFi modules cut-out of 65 mm • Choose only events with high track multiplicity • For bunch measurements: NTr≥ 11 (0.45 TeV); NTr≥ 18 (7 TeV) • For beam measurements: NTr≥ 15 (0.45 TeV); NTr≥ 25 (7 TeV) • In the following: • Estimates of the relative uncertainty on the beam width at 7 TeV (always worse than at 450 GeV, because transverse beam size is smaller) • As function of aperture • And for different tapering angles

  7. Vertex Resolution Definition s = vertex resolution Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Define and track true MC vertex xMCwith BGV toy MC Simulation • Sort events per number of tracks/vertex (NTr) • Reconstruct primary vertex with LHCb algorithm xrec • For each NTrplot histogram with residuals: xMC – xrec • Fit histogram with 3 parameter Gauss Function to obtain s

  8. Vertex Resolution versus NTr Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Divide original vertices from MC simulation in 4 z-position intervals • [-500;-100], [-100;300], [300,700], [700,1100] mm • Sort residuals accordingly • Fit the x and y resolution with function: • Fit convergences very sensitive to the initially given parameter values need to improve fitting method

  9. Vertex Resolution versus NTr (II) Maria Kuhn - BGV Meeting #20 - 25.9.2013

  10. Vertex Resolution versus NTr (III) Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Repeated vertex resolution calculation for all apertures with 75º tapering angle • “Nominal” aperture (23mm) • 2 mm reduced aperture (21 mm) • 4 mm reduced aperture (19 mm)

  11. Weighted Vertex Resolution detector Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Choose events with NTr≥ 18 • Weighted resolution: • With and weights • Vertex resolution improves when going closer to detector • But less high-multiplicity events

  12. Summary Resolution for NTr≥ 18 Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Comparison of weighted vertex resolution for different apertures • resolution error obtained from Gauss fit of histogram (statistical) • Choose events with NTr≥ 18 • Weighted vertex resolution for each NTr≥ 18 • Results for x and y resolutions are similar, quoting the average of x and y • To do: get resolution from curve fit and not from histogram

  13. Conclusion - enorm = 1 mm Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Reminder: with • at 7 TeVfor enorm = 1 mm & b = 170 m

  14. Conclusion - different enorm Maria Kuhn - BGV Meeting #20 - 25.9.2013 • for enorm = 1.5 [2.,2.5] mm • 7 TeV & b = 170 m • Average over z range from [-500;700] mm (discard first z bin)

  15. for Different Emittances Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Relative uncertainty on the transverse beam size • See table on previous slide • Better accuracy for larger transverse beam sizes • Smaller relative beam size uncertainty for smaller aperture

  16. Vertex Resolution for 45º Tapering Angle P. Hopchev Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Repeated these studies with different tapering angle • 45º instead of 75º • 23 mm aperture • NTr≥ 18 • Conclusions: • For every z-position interval the vertex resolution is worse for the smaller tapering angle • The relative uncertainty of the measured beam size improves by 9 % when choosing a larger tapering angle (75º) • Again assuming

  17. Summary Maria Kuhn - BGV Meeting #20 - 25.9.2013 • The expected vertex resolution is estimated from the BGV toy MC • For 3 different apertures: 23 mm, 21 mm, 19 mm (75º tapering angle) • And for 2 different tapering angles: 45º and 75º (23 mm aperture) • The improvements on are • 10 – 15 % better resolution for 2 mm reduced aperture • 20 – 30 % better resolution for 4 mm reduced aperture • With respect to 23 mm aperture • 9 % better resolution for 75º tapering angle • With respect to 45º

  18. Additional Slides Maria Kuhn - BGV Meeting #20 - 25.9.2013

  19. Vertex Resolution for 2 mm Reduced Aperture Maria Kuhn - BGV Meeting #20 - 25.9.2013

  20. Vertex Resolution for 2 mm Reduced Aperture Maria Kuhn - BGV Meeting #20 - 25.9.2013

  21. Vertex Resolution for 4 mm Reduced Aperture Maria Kuhn - BGV Meeting #20 - 25.9.2013

  22. Vertex Resolution for 4 mm Reduced Aperture Maria Kuhn - BGV Meeting #20 - 25.9.2013

  23. Vertex Resolution Nominal Aperture Nominal aperture = 23 mm Maria Kuhn - BGV Meeting #20 - 25.9.2013 • Scatter plot: vertex resolution per z and #tracks bin • Colour represents vertex resolution for x and y position • Circle size represents #events per bin (see previous slide) • Best x and y vertex resolution for large #tracks! • Weighted resolution =

  24. 2mm Reduced Aperture Maria Kuhn - BGV Meeting #20 - 25.9.2013 Aperture = 21 mm Vertex resolution improves

  25. 4 mm Reduced Aperture Maria Kuhn - BGV Meeting #20 - 25.9.2013 Aperture = 19 mm Vertex resolution even better

  26. NTr ≥ 25 Not very useful to analyse – not enough statistics in high track multiplicity bin Maria Kuhn - BGV Meeting #20 - 25.9.2013

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